This invention relates to a method of making a container portion for a sodium sulfur battery in which the elements used are readily available on the commercial market. The method involves the expanding of an outer steel casing in a heating operation so that the casing may be slipped over an inner graphite pipe. Upon cooling, the steel casing shrinks into intimate contact with the graphite pipe.
A novelty study was conducted on the subject matter of this disclosure in the U.S. Patent Office. While the study resulted in the citation of several patents relating to sodium sulfur battery constructions, none of the patents so cited showed a sodium sulfur battery construction in which a heated outer steel casing was subsequently shrunk into engagement with an inner graphite pipe as part of the method of making a portion a container for such a battery.
U.S. Pat. No. 541,507 was cited in the search report. This patent was entitled "Breach Loading Ordinance and Art of Assembling or Disassembling Parts of Same." On page 2, commencing at line 50, the patent describes the process of making guns in which various elements are heated and then shrunk about an unheated element.
The prior art cited does not appear to be of interest with respect to the method of this invention because it does not show shrinking of an expanded steel casing about an inner graphite pipe, that graphite pipe originally being porous in nature. The art also does not teach a subsequent sealing of the porosity of the graphite pipe so that it is not attacked by the molten sodium polysulfide materials which come in contact therewith during operation of the battery.
It is a principal object of this invention to provide a portion of a container for a sodium sulfur battery in which an outer metal casing is brought into contact with an inner graphite pipe in such a manner that under normal operating conditions of the battery, a low electrical resistance path is provided between the outer metal casing and the cathode compartment of the battery.
It is a further object of this invention to provide such a method which uses materials which are readily available on the commercial market.